The use of shunts to measure an electric current flowing in a circuit has a long history. Typically, such current measurements rely on measuring the voltage drop developed across a conductive material when current is sent through the material. For example, if one employs a conductive material having a known resistance R, then a current I flowing through the material may be ascertained by simply measuring the voltage drop V generated across the material by the current flow, and applying Ohm's law: I=V/R.
By knowing the resistance of a fixed volume of conductive material under standard temperature and pressure (STP) conditions, as well as the variation of that resistance with temperature, the conductive material may be used to directly determine the magnitude of the current flowing through the current carrying path.
The conductive material may be used to carry current from a fixed or variable alternating current (AC) or direct current (DC) source to a fixed or variable load. Typical conductive materials, as a consequence of their inherent physical properties, have an electrical resistance characteristic that varies with the material's cross section, length, and temperature. Changes in temperature can therefore impact the accuracy of a current measurement, and need to be compensated for.
In order to measure large currents with reasonably low voltages, shunts are generally constructed to have low resistance. However, depending on the application and current range of interest, this often results in a physically large and therefore undesirable shunt.
To avoid variations in resistance that occur with changes in temperature from introducing error into the current measurement, relatively expensive shunts have been developed, employing alloys that exhibit exceedingly small variations of resistivity with temperature. The most common of these alloys is Manganin, which is comprised of copper, manganese, and nickel. Other alloys, such as Constantan (copper, manganese, nickel), or iron-chrome, or manganese-copper, as well as other proprietary alloys may also be used.
Various electronic means have been devised in the art to compensate for temperature variations in shunt resistance. For example, U.S. Pat. No. 6,028,426 discloses a fixed gain amplifier circuit whose output is attenuated to compensate for temperature effects by using a thermistor whose resistance varies inversely with temperature.
U.S. Pat. No. 5,095,274 discloses a shunt formed from a portion of a circuit board trace and a circuit for compensating temperature changes in shunt resistance by using a diffused resistor with particular characteristics in a comparator circuit.
U.S. Patent Publication 2011/0089931 shows temperature compensation circuitry for current shunts that use thermistors to vary the gain of an amplifier by varying its input resistance, such that the amplifier compensates for temperature variations in the shunt.
However, the prior art does not provide the benefits of the novel shunt and circuit arrangements disclosed herein, as further described below.